EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1112 AM EDT SUN JUL 05 2015 VALID 12Z WED JUL 08 2015 - 12Z SUN JUL 12 2015 ...PATTERN OVERVIEW... AN UPPER LOW OFF THE WEST COAST WILL DRIFT SLOWLY EASTWARD IN THE MEDIUM RANGE BEFORE LIFTING NORTHEASTWARD ONCE IT MOVES INTO CALIFORNIA AND OPENS UP AS IT MOVES ACROSS THE INTERIOR. ONCE IT PASSES INLAND...THERE ARE SEVERAL SOLUTIONS THAT SUGGEST THAT IT WILL ALSO BE ASSOCIATED WITH HEIGHT RISES CENTERED OVER THE ROCKY MOUNTAINS. SOME OF THE ENSEMBLE MEANS...INCLUDING THE GFS/NAEFS HAVE THE TROUGH MOVING LIFTING NORTHEASTWARD AND THEN DROPPING SLIGHTLY OVER THE NORTHERN PLAINS. MEANWHILE THE EUROPEAN ENSEMBLES SUGGEST THAT THE TROUGH CONTINUES NORTHWARD ALONG THE WEST COAST...ALLOWING A STRONGER RIDGE TO DEVELOP OVER THE SOUTHWEST. THESE DIFFERENCES ARE IMPORTANT SINCE THE EVOLUTION OF HOW THIS LIFTING TROUGH EITHER AMPLIFIES A RIDGE OVER THE WEST OR RESULTS IN A FLATTER FLOW OVER THE US WILL HAVE A LARGE IMPACT ON HOW TEMPERATURES/PRECIPITATION EVOLVE LATER IN THE MEDIUM RANGE. EARLY IN THE FORECAST...THE PATTERN REMAINS CONSISTENT WITH THE FORECASTS OVER THE PAST FEW DAYS WITH A COLD FRONT MOVING INTO THE OHIO VALLEY/NORTHEAST ON WEDNESDAY WITH A TRAILING FRONT FROM THE SOUTHERN PLAINS NORTHEASTWARD ACROSS THE MID MISSISSIPPI VALLEY INTO THE OHIO VALLEY BEING A FOCUS FOR SHOWERS AND THUNDERSTORMS. THIS COLD FRONT APPEARS TO STALL OUT FROM THE CENTRAL PLAINS ACROSS THE OHIO VALLEY INTO THE MID ATLANTIC ON THURSDAY...AGAIN PROVIDING A FOCUS FOR SHOWERS/THUNDERSHOWERS...WITH A POSSIBLE WAVE ALONG THE FRONT ALTHOUGH AN EXACT LOCATION IS REALLY HARD TO PINPOINT YET. BY FRIDAY...THE WEAK STATIONARY BOUNDARY SEEMS TO PERSIST AND EXAMINATION OF MANY DIFFERENT SOLUTIONS SUGGEST THAT THE BOUNDARY MAY CONTINUE TO EXIST THROUGH THE END OF THE FORECAST...INCLUDING SUNDAY. OF COURSE...BY DAY 7...SUCH WEAK FEATURES ARE VERY DIFFICULT TO DISCERN WITHIN THE INCREASING SPREAD OF THE MODEL SOLUTIONS. ...GUIDANCE EVALUATION/PREFERENCES... IT APPEARS THAT THE EVOLUTION OF THE WEST COAST CLOSED LOW IS AN IMPORTANT HARBINGER IN HOW THE WEATHER PATTERNS COULD EVOLVE LATER IN THE FORECAST. COMPARING THE MEANS...THE CANADIAN IS THE OUTLIER THAT FAVORS A BUILDING RIDGE IN THE EAST...SUGGESTING A RETURN TO HOT WEATHER. HOWEVER...THE OTHER MODELS ARE MUCH LESS OBVIOUS AND WHILE THE LIFTING OF THE TROUGH ACROSS THE WEST COULD LEAD TO A GENERAL RAISING OF HEIGHTS DOWNSTREAM FROM THE ROCKIES EASTWARD...THE MEANS AND CERTAINLY THE OPERATIONAL RUNS ARE MORE NUANCED. IN GENERAL...THE ECMWF MEMBERS TREND SLOWER WITH THE MOVEMENT OF THE TROUGH TOWARD THE WEST COAST BY DAY 5/FRIDAY WITH THE MEAN UPPER LOW OVER NORTH CENTRAL CALIFORNIA WHILE THE GEFS/NAEFS MEMBERS ARE FASTER WITH THE MEAN LOW ONE STATE EAST OVER NEVADA. AT THIS POINT IN THE FORECAST...THE DIFFERENCES DO NOT APPEAR TO IMPACT THE RESULTING FORECAST MUCH BUT LATER FORECASTS FOR DAYS 6 AND 7 REMAIN HIGHLY UNCERTAIN AS THE IMPACT OF THE LIFTING TROUGH AND DOWNSTREAM HEIGHTS HAVE A LARGE SPREAD OF SOLUTIONS. WITH ALL THE UNCERTAINTY...THERE DOES APPEAR TO BE A TREND IN THE DAY 7/SUNDAY FORECASTS SHOWING A BUILDING RIDGE NOT ONLY IN THE EUROPEANS SOLUTIONS... WITH A HIGH AMPLITUDE RIDGE IN THE 00Z ECMWF OPERATIONAL RUN. BOTH THE GEFS/NAEFS MEANS ALSO SHOW A BUILDING RIDGE OVER THE NORTHERN ROCKIES WITH A REMNANT OF THE WEST COAST TROUGH MOVING EAST OF THE RIDGE AXIS INTO THE NORTHERN PLAINS STATES. IF THE TREND FOR THE BUILDING RIDGE PROVES TO BE SOMEWHAT ACCURATE...THE LIKELIHOOD A BUILDING RIDGE IN THE EAST BECOMES LESS AND LESS. AT PRESENT...THE GEFS/NAEFS SHOW A FAIRLY FLAT FLOW IN THE EAST WHILE THE EUROPEAN MEANS CONTINUE TO POINT TO A WEAK TROUGH IN THE EAST. THESE SORT OF DIFFERENCES WILL HOPEFULLY COME MORE CLEAR AS THE PERIOD DRAWS CLOSER. THE FORECAST TO KEEP THE WEAK STATIONARY FRONT IN THE EAST RELIES ON THE FLAT FLOW REMAINING IN THE EAST AS A COMPROMISE BETWEEN THE EUROPEAN AND GEFS/NAEFS FORECASTS. CYCLONIC FLOW NEAR HUDSON BAY MAINTAINS A FRONTAL SYSTEM CLOSE TO THE US CANADIAN BORDER BUT THE FORECASTS CURRENTLY DO NOT SUGGEST THAT THE FRONT MAKES IT FARTHER SOUTH THAN THE US BORDER FOR THE TIME BEING. A STRONGER COLD FRONT OVER SOUTH CENTRAL CANADA THAN SUGGESTED BY THE MEANS ALLOWED US TO PREFER THE 00Z GFS OVER THE 06Z VERSION IN GENERATING THE GRAPHICS. IN GENERAL...THOUGH...USED A COMPOSITE BLEND OVER THE ENTIRE FORECAST WITH ONLY A MAJORITY OF OPERATIONAL RUNS USED ON DAY 3/WEDNESDAY AND A 50/50 BLEND OF OPERATIONAL/MEANS ON DAYS 4 AND 5/THURSDAY AND FRIDAY WITH LITTLE PREFERENCE FOR ANY ONE MODEL OVER ANOTHER. A SLIGHT PREFERENCE FOR THE ENSEMBLE MEANS OVER THE OPERATIONAL ECMWF/GFS WAS USED FOR DAY 6/SATURDAY WHILE MOST OF THE DAY 7 FORECAST WAS GENERATED BY A COMBINATION OF THE EUROPEAN/GEFS ENSEMBLE MEANS. ...SENSIBLE WEATHER HIGHLIGHTS... HAVE CONTINUED TO EMPHASIZE A FAVORED AREA FOR RAINFALL NEAR THE SURFACE FRONTAL BOUNDARY THAT MAY/MAY NOT CONTINUE INTO NEXT WEEKEND. THIS OCCURS WITH THE FOCUS PROVIDED BY THE PRESENCE OF ONE OR MORE LOW AMPLITUDE SHORTWAVE TROUGHS ALOFT. NORTH OF THE FRONTAL BOUNDARY...COOLER AIR AND THE POSSIBILITY OF RAIN COOLED AIR AS WELL COULD KEEP TEMPERATURES BELOW SEASONAL AVERAGES. HOT AND HUMID CONDITIONS SHOULD PERSIST SOUTH OF THE BOUNDARY BUT SHOULD NOT BE EXCESSIVE AT THIS POINT. THE BIGGER CONCERN IS LATER IN THE FORECAST WHEN THERE IS STILL LARGE UNCERTAINTY. ANY AMPLIFICATION OF A RIDGE WHETHER OVER THE ROCKY MOUNTAINS OR THE SMALLER CHANCE IT OCCURS FARTHER EAST WOULD CERTAINLY INFLUENCE WHERE ANY EXCESSIVE HEAT COULD DEVELOP. GIVEN THE TREND FOR THE MEAN RIDGE TO BUILD RECENTLY OVER THE WEST WOULD MEAN THAT ANY ADDITIONAL RIDGING COULD SEE THE EXTREME HEAT RETURN TO PORTIONS OF THE WEST...ALTHOUGH IT IS MUCH TOO EARLY TO JUMP ON THAT BANDWAGON. MEANWHILE THE UPPER LOW MOVING INTO THE WEST FROM JUST OFF THE CA COAST IS STILL EXPECTED TO ENHANCE RNFL OVER FAVORED TERRAIN INLAND FROM THE CENTRAL WEST COAST AND THEN INTO THE NORTHERN ROCKIES AND POSSIBLY THE PLAINS. ALSO ANTICIPATE ONE OR MORE EPISODES OF CONVECTION WITH VARYING INTENSITY OVER THE CNTRL-SRN ROCKIES AND DIURNAL ACTIVITY OVER PARTS OF THE SOUTHEAST. EVOLUTION OF FLOW ALOFT OVER THE WEST SHOULD SUPPORT A SIGNIFICANT COOLING TREND IN THE NORTHWEST AFTER SOME LOCATIONS SEE HIGHS 10-20F ABOVE NORMAL EARLY IN THE FORECAST. KOCIN